Particular embodiments generally relate to amplifiers.
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
FIG. 1 depicts a conventional amplifier 100. Amplifier 100 is used to amplify a signal input at a node Vin and output at a node Vout. For example, amplifier 100 may be used in a transceiver that receives a radio frequency (RF) signal that is amplified using amplifier 100. A signal path for the RF signal is shown at 102. The signal goes through a first alternating current (AC) coupling capacitor Ca, a transistor M1, a second AC coupling capacitor Cb, and a transistor M2. AC coupling capacitors Ca and Cb couple the AC signal from node Vin to node Vout. Using AC coupling capacitors Ca and Cb require tuning of amplifier 100 to adjust the resonant frequency to suit the frequency band needed for amplifier 100.
Also, a first biasing voltage (VB1) and a second biasing voltage (VB2) are used to bias transistors M1 and M2. Transistors M1 and M2 are biased such that a direct current (DC) current biasing path flows at 104.
Transistor M1 may be isolated from a transistor M2 over a frequency range where amplifier 100 exhibits useful gain. The gain may be in the form of two amplifiers represented by transistor M1 and inductor L1 in one amplifier and transistor M2 and inductor L2 in another. Also, inductor (L1) 108 and a capacitor (Cc) 110 in isolation circuit 106 are used to isolate transistors M1 and M2. For example, isolation circuit 106 has a high impedance and high gain in a narrow frequency range.
FIG. 2 depicts a graph 200 showing an example of the frequency response for the gain of amplifier 100 using isolation circuit 106. The transceiver may operate over a wideband range of frequency, which is from 1 megahertz (MHz) to 1 gigahertz (GHz) in this example. However, a narrow frequency range at 202 is where inductor 108 and capacitor 110 have a high impedance, which isolates transistor M1 from transistor M2. With transceivers operating in a wideband frequency range, the narrow frequency band isolation offered by inductor 108 and capacitor 110 may be insufficient. Thus, a wideband amplifier cannot be offered using amplifier 100 because transistor M1 and transistor M2 are not isolated over a wideband of frequencies.